Polyolefin compositions with improved mechanical and barrier properties

ABSTRACT

Polymer compositions may include a polymer matrix containing a polyolefin, one or more polymer particles dispersed in the polymer matrix, wherein the one or more polymer particles include a polar polymer selectively crosslinked with a crosslinking agent, and wherein the one or more polymer particles has an average particle size of up to 200 μm. Processes of preparing a polymer composition may include mixing a polyolefin, a polar polymer, and a crosslinking agent; and selectively crosslinking the polar polymer with the crosslinking agent in the presence of the polyolefin. Methods may include increasing stress cracking resistance of a polyolefin by mixing a polar polymer with the polyolefin; and selectively crosslinking the polar polymer in the presence of the polyolefin with a crosslinking agent to form crosslinked polar polymer particles dispersed in the polyolefin.

BACKGROUND

Polyolefins such as polyethylene (PE) and polypropylene (PP) may be usedto manufacture a varied range of articles, including films, moldedproducts, foams, and the like. Polyolefins may have characteristics suchas high processability, low production cost, flexibility, low densityand recycling possibility. However, physical and chemical properties ofpolyolefin compositions may exhibit varied responses depending on anumber of factors such as molecular weight, distribution of molecularweights, content and distribution of comonomer (or comonomers), methodof processing, and the like.

Methods of manufacturing may utilize polyolefin's limited inter- andintra-molecular interactions, capitalizing on the high degree of freedomin the polymer to form different microstructures, and to modify thepolymer to provide varied uses in a number of technical markets.However, polyolefin materials may have a number of limitations, whichcan restrict application such as susceptibility to deformation anddegradation in the presence of some chemical agents, and low barrierproperties to various gases and a number of volatile organic compounds(VOC). Property limitations may hinder the use of polyolefin materialsin the production of articles requiring low permeability to gases andsolvents, such as packaging for food products, chemicals, agrochemicals,fuel tanks, water and gas pipes, and geomembranes, for example.

While polyolefins are utilized in industrial applications because offavorable characteristics such as high processability, low productioncost, flexibility, low density, and ease of recycling, polyolefincompositions may have physical limitations, such as susceptibility toenvironmental stress cracking (ESC) and accelerated slow crack growth(SCG). Which may occur below the yield strength limit of the materialwhen subjected to long-term mechanical stress. Polyolefin materials mayalso exhibit sensitivity to certain groups of chemical substances, whichcan lead to deformation and degradation. As a result, chemicalsensitivities and physical limitations may limit the success in thereplacement of other industry standard materials, such as steel andglass, with polyolefin materials because the material durability isinsufficient to prevent chemical damage and spillage.

Conventionally, methods of altering the chemical nature of the polymercomposition may include modifying the polymer synthesis technique or theinclusion of one or more comonomers. However, modifying the polyolefinmay also result in undesirable side effects. By way of illustration,increasing the molecular weight of a polyolefin may produce changes inthe SCG and ESC, but can also increase viscosity, which may limit theprocessability and moldability of the polymer composition.

Other strategies may include inclusion of a comonomer and/or blendingpolyolefins with other polymer classes and additives to confer variousphysical and chemical attributes. For example, polyolefins may becopolymerized with alpha-olefins having a lower elastic modulus, whichresults in a considerable increase in environmental stress crackingresistance (ESCR) and resistance to impact but adversely affects thestiffness of the polymer. However, the use of alpha-olefins may havelimited effectiveness because, while the incorporation of alpha-olefincomonomers must occur in the high molecular weight fraction in order toaffect ESC and impact resistance, many popular catalyst systems have alow probability of inserting alpha-olefins in the high molecular weightfraction, an important factor in forming “tie molecules” between thechains of the surrounding polyolefin that are responsible fortransferring stress between the crystalline regions and, consequently,responsible for important mechanical properties. The end result is theproduction of a polymer composition having reduced structural stiffness.It is also noted that, while advances have developed catalysts thatincrease the likelihood of displacing the incorporation of a comonomerto the highest molecular weight range, and that multiple reactors may beused to address these limitations, such modifications are expensivealternatives and not wholly effective in balancing resistance to impactand ESC without negatively affecting stiffness.

Polymer modification by blending may vary the chemical nature of thecomposition, resulting in changes to the overall physical properties ofthe material. Material changes introduced by polymer blending may beunpredictable, however, and, depending on the nature of the polymers andadditives incorporated, the resulting changes may be uneven and somematerial attributes may be enhanced while others exhibit notabledeficits. The incorporation of a second phase into the matrix polymer,which generally has a different chemical nature, may increase theresistance to impact and ESC resistance in some cases. However, like thecopolymerization strategy, polymer blends are often accompanied by amarked loss in stiffness, because the blended materials may have lowerelastic modulus than the matrix polyolefin.

Accordingly, were exists a continuing need for developments inpolyolefin compositions to have increases in environmental stresscracking resistance while balancing the mechanical properties of thepolymer. There also exists a continuing need for polyolefin compositionshaving good barrier properties to various gases and volatile organiccompounds.

SUMMARY

This summary is provided to introduce a selection of concepts that aredescribed further below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments of the present disclosure are directed topolymer compositions that may include a polymer matrix containing apolyolefin, one or more polymer particles dispersed in the polymermatrix, wherein the one or more polymer particles include a polarpolymer selectively crosslinked with a crosslinking agent, and whereinthe one or more polymer particles has an average particle size of up to200 μm.

In another aspect, embodiments of the present disclosure are directed toprocesses of preparing a polymer composition may include mixing apolyolefin, a polar polymer, and a crosslinking agent; and selectivelycrosslinking the polar polymer with the crosslinking agent in thepresence of the polyolefin.

In another aspect, embodiments of the present disclosure are directed tomethods that may include increasing stress cracking resistance of apolyolefin by mixing a polar polymer with the polyolefin; andselectively crosslinking the polar polymer in the presence of thepolyolefin with a crosslinking agent to form crosslinked polar polymerparticles dispersed in the polyolefin.

Other aspects and advantages of the disclosure will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1 and 2 are scanning electron micrographs (SEMs), before and afterboiling respectively, of a comparative sample of polyolefin containing anon-crosslinked polar polymer in accordance with embodiments of thepresent disclosure.

FIGS. 3-5 are SEMs of polymer compositions containing polyolefin andcrosslinked polar polymer in accordance with embodiments of the presentdisclosure.

FIG. 6 is a graphical representation depicting the change inenvironmental stress cracking resistance (ESCR) as a function ofpolyvinyl alcohol (PVOH) content in accordance with embodiments of thepresent disclosure.

FIG. 7 is a graphical representation depicting the property balanceindex (PBI) for a number of polymer compositions generated in accordancewith embodiments of the present disclosure.

FIG. 8 is a graphical representation depicting changes in PBI forpolymer compositions generated in accordance with embodiments of thepresent disclosure.

FIG. 9 is a graphical representation depicting relative changes in FBIfor selected polymer composition samples generated in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to polymercompositions containing a mixture of polyolefin and polar polymerparticles. In one or more embodiments, polymer composition may include amatrix polymer phase containing polyolefin and one or more polar polymerparticles dispersed in the matrix phase, where the polar polymer iscrosslinked with a crosslinking agent that reacts selectively withfunctional groups present on the constituent polar polymer. In someembodiments, crosslinks generated in the polar polymer particles by thecrosslinking agent may create structural and/or morphological changesthat produce a polymer composition exhibiting significantly improvedphysical and chemical characteristics when compared to a referencecomposition containing only the respective polyolefin. For example,polymer compositions in accordance with the present disclosure mayexhibit gains in environmental stress cracking resistance, while alsomaintaining a balance of mechanical properties and may also conferimproved barrier properties to gases and liquids.

In one or more embodiments, polyolefins may be blended with a polarpolymer to adjust various physical and chemical properties of the finalcomposition. Specifically, in one or more embodiments, physical andchemical properties of polymer compositions in accordance with thepresent disclosure may be modified by blending the polyolefin with apolar polymer having one or more functional groups that are selectivelyreacted with crosslinking agents, where the crosslinking occurs as orafter the polyolefin and polar polymer are blended together, i.e., inthe presence of but without reacting with the polyolefin. In someembodiments, in the blended polymer composition, the polar polymer maybe in the form of sized particles having dimensions, such as less than200 μm, suitable for end use applications. Thus, in the blended polymercomposition, the polar polymer particles may be dispersed within apolyolefin matrix phase. Optionally, a functionalized polyolefin may beadded as a compatibilizing agent, in addition to other additives.Processes of manufacturing polymer compositions in accordance with thepresent disclosure may include various blending methods such asolubilization, emulsion, suspension or extrusion.

In some embodiments, the polar polymer within the polymer compositionmay be crosslinked by a crosslinking agent to generate particulatescontaining intraparticle covalent linkages between the constituent polarpolymer chains. Depending on the relative proximity of adjacent polarpolymer particles (and concentration), it is also recognized that theremay also be inter-particle covalent linkages that are formed. Thecrosslinked polar polymer particles may create changes in the physicaland physicochemical properties, including increases in ESCR, increasesin barrier to oxygen and volatile organic compounds (VOC), andimprovement in the balance of stiffness/impact resistance mechanicalproperties in relation to the properties of pure (unmodified or blended)polyolefins. The balance in properties may be expressed through aproperty balance index, which considers the combination of the flexuralmodulus, impact resistance and ESCR, discussed in greater detail below.The property balance index may be normalized against a referencepolyolefin (without the polar polymer, etc.), and advantageously, thepolymer compositions of the present disclosure may achieve a normalizedproperty balance index that ranges from about 1.5 to 10, or from 3 to 6in more particular embodiments.

In one or more embodiments, polymer compositions may be used in themanufacturing of articles, including rigid and flexible packaging forfood products, chemicals, agrochemicals, fuel tanks, water and gaspipes, geomembranes, and the like.

Polyolefin

Polyolefin in accordance with the present disclosure may form a polymermatrix that surrounds other components in the polymer composition suchas polar polymer particles and other additives. In one or moreembodiments, polyolefins include polymers produced from unsaturatedmonomers (olefins or “alkenes”) with the general chemical formula ofC_(n)H_(2n). In some embodiments, polyolefins may include ethylenehomopolymers, copolymers of ethylene and one or more C3-C20alpha-olefins, propylene homopolymers, heterophasic propylene polymers,copolymers of propylene and one or more comonomers selected fromethylene and C4-C20 alpha-olefins, olefin terpolymers and higher orderpolymers, and blends obtained from the mixture of one or more of thesepolymers and/or copolymers.

In one or more embodiments, polymer compositions may contain a percentby weight of the total composition (wt %) of polyolefin ranging from alower limit selected from one of 30 wt %, 40 wt %, 50 wt %, 60 wt %, 75wt %, and 85 wt %, to an upper limit selected from one of 60 wt %, 75 wt%, 80 wt %, 90 wt %, 95 wt %, 99.5 wt % and 99.9 wt %, where any lowerlimit can be used with any upper limit.

Polar Polymers

Polymer compositions in accordance with the present disclosure mayinclude one or more polar polymers that are combined with a polyolefinand, further, may be crosslinked by one or more crosslinking agents. Asused herein, a “polar polymer” is understood to mean any polymercontaining hydroxyl, carboxylic acid, carboxylate, ester, ether,acetate, amide, amine, epoxy, imide, imine, sulfone, phosphone, andtheir derivatives, as functional groups, among others. The polar polymermay be selectively crosslinked by an appropriate crosslinking agent,where the selective crosslinking may occur between the functional groupsby reacting with a suitable crosslinking agent in the presence ofpolyolefins, additives, and other materials. Thus, the crosslinkingagent is selected to react with the polar polymer but without exhibitingreactivity (or having minimal reactivity towards) the polyolefin(including any functionalized polyolefins present as a compatibilizingagent, discussed below). In some embodiments, polar polymers includepolyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) copolymer,ethylene vinyl acetate copolymer (EVA) and mixtures thereof.

One or more polar polymers in accordance with the present disclosure maybe produced by hydrolyzing a polyvinyl ester to produce free hydroxylgroups on the polymer backbone. By way of example, polar polymersproduced through hydrolysis may include polyvinyl alcohol generated fromthe hydrolysis of polyvinyl acetate. The degree of hydrolysis for apolymer hydrolyzed to produce a polar polymer may be within the range of30% and 100% in some embodiments, and between 70% and 99% in someembodiments.

Polar polymers in accordance with the present disclosure may have aweight average molecular weight in the range of 5,000 g/mol to 300,000g/mol in some embodiments, and between 10,000 g/mol and 180,000 g/mol insome embodiments.

In one or more embodiments, polar polymer in accordance with the presentdisclosure may form a distinct phase within the polymer composition,which may be in the form of particles having an average particle size ofless than 200 μm. Particle size determinations may be made in someembodiments using SEM techniques after the combination with thepolyolefin. Polar polymer particles in accordance with the presentdisclosure may have an average particle size having a lower limitselected from 0.01 μm, 0.5 μm, 1 μm, and 5 μm, and an upper limitselected from 10 μm, 20 μm, 30 μm, 50 μm, and 200 μm, where any lowerlimit may be used with any upper limit.

In one or more embodiments, polymer compositions may contain a percentby weight of the total composition (wt %) of polar polymer ranging froma lower limit selected from one of 0.1 wt %, 0.25 wt %, 0.5 wt %, 1 wt%, 2 wt %, 5 wt %, 10 wt %, 15 wt %, and 25 wt %, to an upper limitselected from one of 5 wt %, 10 wt %, 15 wt %, 25 wt %, 50 wt %, 60 wt%, and 70 wt %, where any lower limit can be used with any upper limit.

Functionalized Polyolefin

In some embodiments, compatibilizing agents such as functionalizedpolyolefins may be added to modify the interactions between thepolyolefin and the polar polymer. As used herein, “functionalizedpolyolefin” (or compatibilizing agent) is understood to mean anypolyolefin which had its chemical composition altered by grafting orcopolymerization, or other chemical process, using polar functionalizingreagents. Functionalized polyolefins in accordance with the presentdisclosure include polyolefins functionalized with maleic anhydride,maleic acid, acrylic acid, methacrylic acid, itaconic acid, itaconicanhydride, methacrylate, acrylate, epoxy, silane, succinic acid,succinic anhydride, ionomers, and their derivatives, or any other polarcomonomer, and mixtures thereof, produced in a reactor or by grafting.

In one or more embodiments, polymer compositions may contain a percentby weight of the total composition (wt %) of functionalized polyolefinranging from a lower limit selected from one of 0.1 wt %, 0.5 wt %, 1 wt%, and 5 wt %, to an upper limit selected from one of 5 wt %, 7.5 wt %,10 wt %, and 15 wt %, where any lower limit can be used with any upperlimit.

Crosslinking Agent

In one or more embodiments, a crosslinking agent may be used tocrosslink a selected polymer phase in a polymer composition. As usedherein, a “crosslinking agent” is understood to mean any bi- ormulti-functional chemical substance capable of reacting selectively withthe polar groups of a polymer, forming crosslinks between and within theconstituent polymer chains. As used herein, “selective” or “selectively”used alone or in conjunction with “crosslinking” or “crosslinked” isused to specify that the crosslinking agent reacts exclusively with thepolar polymer, or that the crosslinking agent reacts with the polarpolymer to a substantially greater degree (98% or greater, for example)than with respect to the polyolefin polymer.

In one or more embodiments, crosslinking agents in accordance with thepresent disclosure may include linear, branched, saturated, andunsaturated carbon chains containing functional groups that react withcounterpart functional groups present on the backbone and termini of apolar polymer incorporated into a polymer composition. In someembodiments, crosslinking agents may be added to a pre-mixed polymerblend containing a polyolefin and polar polymer particles, in order tocrosslink the polar polymer in the presence of the polyolefin. Followingaddition to the pre-mixed polymer blend, a crosslinking agent may reactwith the polar polymer within the particles, creating intraparticlecrosslinks between the polar polymer chains. Crosslinking agents inaccordance with the present disclosure may include, for example, maleicanhydride, maleic acid, itaconic acid, itaconic anhydride, succinicacid, succinic anhydride, succinic aldehyde, adipic acid, adipicanhydride, phthalic anhydride and acids thereof, glutaraldehyde, theirderivatives and mixtures thereof.

In one or more embodiments, crosslinking agents may be added to a blendused to form a polymer composition at a percent by weight (wt %) of theblend ranging from a lower limit selected from one of 0.001 wt %, 0.01wt %, 0.05 wt %, 0.5 wt %, 1 wt %, and 2 wt % to an upper limit selectedfrom one of 1.5 wt %, 2 wt %, 5 wt %, and 10 wt %, where any lower limitcan be used with any upper limit.

Additives

In one or more embodiments, the polymer compositions of the presentdisclosure may contain a number of other functional additives thatmodify various properties of the composition such as antioxidants,pigments, fillers, reinforcements, adhesion-promoting agents, biocides,whitening agents, nucleating agents, anti-statics, anti-blocking agents,processing aids, flame-retardants, plasticizers, light stabilizers, andthe like.

Polymer compositions in accordance with the present disclosure mayinclude fillers and additives that modify various physical and chemicalproperties when added to the polymer composition during blending. In oneor more embodiments, fillers and nanofillers may be added to a polymercomposition to increase the barrier properties of the material byincreasing the tortuous path of the polymer matrix for the passage ofpermeate molecules. As used herein, “nanofiller” is defined as anyinorganic substance with at least a nanometric, scale dimension. Polymercomposition in accordance with the present disclosure may be loaded witha filler and/or nanofiller that may include polyhedral oligomericsilsesquioxane (POSS), clays, nanoclays, silica particles, nanosilica,calcium nanocarbonate, metal oxide particles and nanoparticles,inorganic salt particles and nanoparticles, and mixtures thereof.

Fillers and/or nanofillers in accordance with the present disclosure maybe incorporated into a polymer composition at a percent by weight (wt %)that ranges from 0.001 wt % and 5 wt % in some embodiments, and from 0.1wt % to 2 wt % in some embodiments.

In one or more embodiments, polymer compositions may contain a percentby weight of the total composition (wt %) of one or more additivesranging from a lower limit selected from one of 0.001 wt %, 0.01 wt %,0.05 wt %, 0.5 wt %, and 1 wt %, to an upper limit selected from one of1.5 wt %, 2 wt %, 5 wt %, and 7 wt %, where any lower limit can be usedwith any upper limit.

Polymer compositions in accordance with the present disclosure may beformulated as a “masterbatch” in which the polymer composition containsconcentrations of polar polymer that are high relative to the polarpolymer concentration in a final polymer blend for manufacture or use.For example, a masterbatch stock may be formulated for storage ortransport and, when desired, be combined with additional polyolefin orother materials in order to produce a final polymer composition havingconcentration of constituent components that provides physical andchemical properties tailored to a selected end-use.

One or more of the wt % values mentioned above with respect to each ofthe components refer in fact to amounts that may be used to form such amasterbatch. In one or more embodiments, a masterbatch polymercomposition may contain a percent by weight of the total composition (wt%) of crosslinked polar polymer ranging from a lower limit selected fromone of 10 wt %, 20 wt % 25 wt %, 30 wt %, 40 wt %, and 50 wt % to anupper limit selected from one of 50 wt %, 60 wt %, and 70 wt %, whereany lower limit can be used with any upper limit. Similarly, amasterbatch may include a polyolefin in an amount that ranges from alower limit selected from 30 wt %, 40 wt %, and 50 wt % to an upperlimit selected from one of 50 wt %, 60 wt %, 70 wt %, 75 wt %, 80 wt %,and 90 wt %, where any lower limit can be used with any upper limit. Itis also envisioned that the functionalized polyolefin may be present atan amount ranging from a lower limit selected from one of 0.1 wt %, 0.5wt %, 1 wt %, and 5 wt %, to an upper limit selected from one of 5 wt %,7.5 wt %, 10 wt %, and 15 wt %, where any lower limit can be used withany upper limit. Fillers or other additives may also be included, asdescribed above.

As noted, in the masterbatch composition, the polymer compositioncontains concentrations of polar polymer that are high relative to thepolar polymer concentration in a final polymer blend for manufacture oruse. Thus, prior to use to form a manufactured article, the masterbatchcomposition may be combined with an additional quantity of polyolefin toarrive at a polar polymer concentration in the final composition that islower than the masterbatch concentration. Further, when it is desirableto form a manufactured article without use of a masterbatch composition,the lower quantities of crosslinked polar polymer and higher quantitiesof polyolefin (from the ranges mentioned above) may be used.

For example, a polymer composition that is to be used directly in themanufacture of a manufactured article, without additional polyolefinadded thereto, may contain a percent by weight of the total composition(wt %) of crosslinked polar polymer ranging from a lower limit selectedfrom one of 0.5 wt %, 1 wt %, 2 wt %, and 5 wt %, to an upper limitselected from one of 5 wt %, 6 wt %, 8 wt %, 10 wt %, 15 wt %, 25 wt %,and 50 wt %, where any lower limit can be used with any upper limit.Similarly, such composition may include a polyolefin in an amount thatranges from a lower limit selected from 50 wt %, 75 wt %, 85 wt %, and90 wt % to an upper limit selected from one of 85 wt %, 90 wt %, 95 wt%, 98 wt %, 99 wt %, and 99.5 wt %, where any lower limit can be usedwith any upper limit. It is also envisioned that the functionalizedpolyolefin may be present at an amount ranging from a lower limitselected from one of 0.1 wt %, 0.5 wt %, 1 wt %, 2 wt %, and 5 wt %, toan upper limit selected from one of 5 wt %, 7.5 wt %, 10 wt %, where anylower limit can be used with any upper limit. Fillers or other additivesmay also be included, as described above.

Polymer Composition Preparation Methods

Polymer compositions in accordance with the present disclosure may beprepared by a number of possible polymer blending and formulationtechniques, which will be discussed in the following sections.

Solubilization

Polymer compositions in accordance with the present disclosure may beprepared from the constituent components using a number of techniques.In one or more embodiments, a matrix polymer (and functionalizedpolyolefin in some cases) are solubilized in a suitable organic solventsuch as decalin, 1,2-dichlorobenzene, 1,1,1,3,3,3-hexafluor isopropanol,and the like. The solvent mixture may then be heated to a temperature,such as between 23° C. and 130° C., under stirring. In parallel, a polarpolymer is solubilized in a suitable organic solvent and temperature.Next, both the matrix polymer solution and the polar polymer solutionare mixed under stirring and a crosslinking agent is added toselectively crosslink the polar polymer, forming dispersed particles ofcrosslinked polar polymer in a polyolefin matrix.

Extrusion

In one or more embodiments, polymer compositions in accordance with thepresent disclosure may be prepared using continuous or discontinuousextrusion. Methods may use single-, twin- or multi-screw extruders,which may be used at temperatures ranging from 100° C. to 270° C. insome embodiments, and from 140° C. to 230° C. in some embodiments. Insome embodiments, raw materials are added to an extruder, simultaneouslyor sequentially, into the main or secondary feeder in the form ofpowder, granules, flakes or dispersion in liquids as solutions,emulsions and suspensions of one or more components.

The components can be pre-dispersed in prior processes using intensivemixers, for example. Inside an extrusion equipment, the components areheated by heat exchange and/or mechanical friction, the phases are meltand the dispersion occurs by the deformation of the polymer. In someembodiments, one or more compatibilizing agents (such as afunctionalized polyolefin) between polymers of different natures may beused to facilitate and/or reline the distribution of the polymer phasesand to enable the formation of the morphology of conventional blendand/or of semi-interpenetrating network at the interface between thephases. The crosslinking agent can be added at the same extrusion stageor in a consecutive extrusion, according to selectivity and reactivityof the system.

In one or more embodiments, methods of preparing polymer compositionsmay involve a single extrusion or multiple extrusions following thesequences of the blend preparation stages. Blending and extrusion alsoinvolve the selective crosslinking of the polar polymer in the dispersedphase of the polymer composition by the crosslinking agent.

Extrusion techniques in accordance with the present disclosure may alsoinvolve the preparation of a polar polymer concentrate (a masterbatch),combined with a crosslinking agent in some embodiments, that is thencombined with other components to produce a polymer composition of thepresent disclosure. In some embodiments, the morphology of a crosslinkedpolar polymer may be stabilized by crosslinking when dispersed in apolymer matrix containing polyolefins and is not dependent on subsequentprocesses for defining the morphology.

Polymer compositions prepared by extrusion may be in the form ofgranules that are applicable to different molding processes, includingprocesses selected from extrusion molding, injection molding,thermoforming, cast film extrusion, blown film extrusion, foaming,extrusion blow-molding, ISBM (Injection Stretched Blow-Molding),rotomolding, pultrusion, and the like, to produce manufactured articles.

EXAMPLES

In the following examples, a number of polymer samples are analyzed todemonstrate the changes in physical and chemical properties associatedwith polymer compositions prepared in accordance with the presentdisclosure.

Characterization Techniques

Prepared samples were characterized using a number of standardized andlab-based polymer characterization techniques discussed below.

Permeability to Volatile Organic Compounds (VOC)

Samples were hot pressed in accordance with ASTM D-4703 on 250 micronthick films. Permeation to the VOC generated by a mixture of toluene andisooctane at a ratio of 1:1 by volume was evaluated by the pervaporationmethod using internally developed equipment. The pervaporation systemincludes a cell having a permeation area of 45 cm² into which a samplefilm was placed separating the cell into two compartments, one keptunder positive pressure with the VOC feed, and the second under vacuum.The permeated vapor was cooled and collected in Dewar flasks andgravimetrically determined. The pervaporation tests were carried out ata temperature of 40° C. The relative barrier values were calculatedbased on the results of permeation for the respective unmodifiedpolyolefin reference.

In one or more embodiments, polymer compositions in accordance withpresent disclosure may exhibit up to 60% increase in barrier to VOC whencompared to a reference polyolefin.

Permeability to Oxygen

Samples were hot pressed on films in accordance with ASTM D-4703 and thepermeability rate to oxygen in stationary state was determined inaccordance with ASTM F-1927 using OX-TRAN® Model MH2/21 oxygentransmission rate test equipment from Mocon, Inc., equipped with acoulometric sensor. The relative barrier values were calculated based onthe results of permeation for the respective unmodified polyolefinreference.

In one or more embodiments, polymer compositions in accordance withpresent disclosure may exhibit up to 60% increase in barrier strength tooxygen when compared to a reference polyolefin according to ASTM F-1927.

Environmental Stress Cracking Resistance (ECR)

For environmental stress cracking resistance tests, sample formulationswere hot pressed in 3 mm thick plaques according to ASTM D-4703, at 200°C. and under pressure. Samples were notched, bent to achieve deformationand placed in a metal U-shaped specimen holder in accordance with ASTMD-1693, and placed in an aqueous solution containing nonylphenolethoxylate (IGEPAL™ CO-630 from Solvay) at a percent by volume (vol %)of 10 vol %. Failure was determined as the appearance of any crackvisible by the naked eye.

Flexural Modulus

The stiffness of the material given by the secant modulus at 1% ofdeformation was determined in the flexural resistance test in accordancewith ASTM D-790. The samples were previously hot pressed in accordancewith ASTM D-4703.

IZOD Impact Resistance Test

The samples were hot pressed in accordance with ASTM D-4703 to carry outthe IZOD resistance to impact standardized by ASTM D-256.

Scanning Electron Microscopy (SEM)

Particle size may be determined by calculating relevant statistical dataregarding particle size. In some embodiments, SEM imaging may be used tocalculate particle size and develop size ranges using statisticalanalysis known for polymers and blends. Samples were examined using SEMafter hot pressing the samples in accordance with ASTM D-4703 andpolishing by cryo-ultramicrotomy. When indicated, some samples weresubmitted to the extraction process of the polar phase (PVOH) bycontacting the sample with boiling water for 2 hours. Samples were driedand submitted to metallization with gold. The images were obtained byFESEM (Field Emission Scanning Electron Microscopy, Model Inspect F50,from FEI), or by Tabletop SEM (Model TM-1000, from Hitachi). The size ofeach polar polymer domain, or particle when selectively crosslinked bythe crosslinking agent, is measured from these images using the softwareLAS (version 43, from Leica). Calibration is performed using the scalebar of each image and the measured values are statistically analyzed bythe software. The average value and standard deviation are given by themeasurement of, at least, 300 particles or domains.

Definition of the Property Balance Index

Changes in physical and chemical properties of polymer compositions inaccordance with the present disclosure are characterized using an indexof properties that may be used to quantify the changes in a respectivepolymer composition based on a balance of mechanical and ESCRproperties. Improvements in a material's modulus, resistance to impactand ESCR may translate to better performance in various applications.However, improvements in a single property may be offset by losses inother properties. In order to quantify the overall improvement of thematerial, the product of the individual properties is monitored in theexamples below. The “Property Balance Index” (FBI) is defined as shownin Eq. 1 to quantify the property changes, wherein “FM” is the flexuralsecant modulus at 1% deformation, “IR” is the IZOD resistance to impactat 23° C., and “ESCR” is the environmental stress cracking resistance.

$\begin{matrix}{{PBI} = \frac{{FM} \times {IR} \times {ESCR}}{10^{7}}} & (1)\end{matrix}$

Definition of the Normalized Property Balance Index

To compare the magnitude of property changes for different polymersystems, the PBI values were normalized according to Eq. 2, whereN_(PBI) is the normalized property balance index, PBI_(sample) is theproperty balance index obtained for the samples of this selectivereaction blend technology and PBI_(reference) is the property balanceindex obtained for the reference samples, i.e., a polymer compositioncomprising the polyolefin used in the sample.

$\begin{matrix}{N_{PBI} = \frac{{PBI}_{sample}}{{PBI}_{reference}}} & (2)\end{matrix}$

Polymer compositions in accordance with the present disclosure mayexhibit an N_(PBI) falling within the range of 1 to 10 in someembodiments, and within the range of 3 to 6 in some embodiments.

Sample Polymer Compositions

Materials used in the example formulations are shown in Table 1, wherethe polyolefins studied include high density polyethylene (HDPE) andlinear low density polyethylene (LLDPE); compatibilizing agents includeHDPE functionalized with maleic anhydride (HDPE-MAH) and low densitypolyethylene functionalized with maleic anhydride (LDPE-MAH); polarpolymers studied include polyvinyl alcohol (PVOH); and crosslinkingagents include maleic anhydride.

TABLE 1 Materials used in examples. 1F (g/10 min 190° C., Distribution21.6 kg of Density ASTM- Molecular (g/cm³) Materials D1238 WeightD1505/D792 Remarks HDPE 1 0.30 Monomodal 0.95 — HDPE 2 0.21 Bimodal 0.95— HDPE 3 0.34 Bimodal 0.96 — LLDPE 1.0 Monomodal 0.92 — HDPE-MAH 4.0 —0.95 — LDPE-MAH 8.0 — 0.93 — Polyvinyl — — 1.3 Degree of alcoholhydrolysis: (PVOH) 99% Crosslinking — — — Maleic agent anhydride

Table 2 presents the formulations analyzed in the following examples,including the method of preparation of the polymer compositions, whereinthe method of preparation is designated “S” for solubilization and “E”refers to extrusion blending “Reference” samples describe polymercompositions containing only polyolefin without the addition of polarpolymer, compatibilizing agents, and crosslinking agents. “Comparative”samples refer to the simple blends, containing polyolefin, polarpolymer, and compatibilizing agent, without adding the crosslinkingagent Formulations denoted “Sample” are compositions containing mixturesof polyolefin and polar polymer that have been selectively crosslinkedby a crosslinking agent. The N_(PBI) values demonstrating the increasein physical properties over the respective reference polymers are alsopresented in Table 2.

TABLE 2 Sample formulations Base PVOH Compatibilizing CrosslinkingSamples S/E Resin (wt %) agent (wt %) agent (wt %) N_(PBI) Reference 1-SS HDPE 1 0 0 0 1 Reference 1-E E HDPE 1 0 0 0 1 Reference 2-E E LLDPE 00 0 1 Reference 3-E E HDPE 2 0 0 0 1 Reference 4-E E HDPE 3 0 0 0 1Comparative A-S S HDPE 1 5 10 0 — Comparative B-E E HDPE 1 7 10 0 0.28Comparative C-E E HDPE 1 7 1 0 0.62 Sample 1-A-S S HDPE 1 5 10 2 —Sample 1-B-E E HDPE 1 7 10 3 1.5 Sample 1-C-S S LLDPE 7 10 3 — Sample1-D-E E LLDPE 7 10 3 — Sample 2-A-E E HDPE 1 7 1 3 5.7 Sample 3-A-E EHDPE 1 7 1 0.5 5.7 Sample 3-B-E E HDPE 1 7 1 1 — Sample 3-C-E E HDPE 1 71 1.5 5.7 Sample 4-B-E E HDPE 1 3 1 0.5 3.4 Sample 4-C-E E HDPE 1 5 10.5 4.8 Sample 5-A-E E HDPE 2 7 1 0.5 6.5 Sample 6-A-E E HDPE 3 7 1 0.53.4

Sample Preparation

Solubilization

In order to prepare samples by solubilization, the polymers,crosslinking agent and other additives were combined in a suitableorganic solvent such as 1,2-dichlorobenzene or N-methyl-2-pyrrolidone,followed by solvent evaporation.

Extrusion

In order to prepare samples by extrusion, the polymers, crosslinkingagents and additives were combined and extruded in a corotatinginterpenetrating twin screw extruder with temperature profile rangingfrom 150 to 230° C., followed by pelletization, and hot pressing filmsor plaques.

Example 1

Samples were formulated as described in Table 2 and evaluated usingvarious methods. For the purpose of comparison of barrier results, thepure (unmodified and unblended) polymers are represented as 0% ofbarrier improvement, having no gains. Reference compositions and resultsare shown in Table 3. Comparative formulations containing a blend ofpolyolefin and polar polymer (without crosslinking) are shown in Table4. Sample polymer compositions were also prepared from a blend ofpolyolefin, polar polymer, and crosslinking agent as shown in Table 5.

TABLE 3 Reference compositions and analysis results. ASTM- Internal ASTMASTM 1927 method ASTM D-790 D-256 Barrier Barrier D-1693 Flexural IZODimpact to O2 to VOC ESCR modulus resistance at Samples (%) (%) (h) (MPa)23° C. (J/m) Reference 1-S — 0 — — — Reference 1-E — 0 180 1273 313Reference 2-E 0 — — — — Reference 3-E — — 150 1100 168 Reference 4-E — — 14 1629 159

TABLE 4 Comparative compositions and analysis results. ASTM- InternalASTM ASTM 1927 method ASTM D-790 D-256 Barrier Barrier D-1693 FlexuralIZOD impact to O2 to VOC ESCR modulus resistance at Samples (%) (%) (h)(MPa) 23° C. (J/m) Comparative A-S — 13 — — — Comparative B-E — 2 1101076 170 Comparative C-E — 1 95.7 1282 356

TABLE 5 Sample compositions and analysis results. ASTM- Internal ASTMASTM 1927 method ASTM D-790 D-256 Barrier Barrier D-1693 Flexural IZODimpact to O2 to VOC ESCR modulus resistance at Samples (%) (%) (h) (MPa)23° C. (J/m) Sample 1-A-S — 50 — — — Sample 1-B-E — 34 600 1058 168Sample 1-C-S 49 — — — — Sample 1-D-E 27 — — — —

By comparison of Tables 3 and 4, it can be noted that the simple blendwith PVOH generates very minor barrier gains (Comparative BE and A-S),even when prepared in solution. Also noted is that the presence of acompatibilizing agent appears to drastically decrease the stiffness ofthe resin (Comparative B-E, when compared to Reference 1-E). With thereduction of the compatibilizing agent content (Comparative C-E), themechanical properties remain stable with respect to Reference 1-E.Regarding ECR of the samples, the simple blend of HDPE with PVOH(Comparative C-E) generates significant loss in this property comparedto Reference 1-E, which is then improved with the use of a crosslinkingagent (Sample 3-A-E from Table 5, for example).

With particular respect to Table 5, a comparison was also performedbetween samples prepared by solubilization (Reference 1-S, ComparativeA-S, and Sample 1-A-S) and extrusion of the components in the presenceof crosslinking agent (Reference 1-E, Comparative C-E, AND Sample 3-A-E,for example). Samples prepared by solubilization and extrusion appearedto exhibit improved barrier properties, and it was noted generally thatlarger improvements were associated with formulations prepared bysolubilization. Sample 1-B-E also exhibited a significant gain in ESCR(600 hours) even compared to respective Reference 1-E (180 hours).

Example 2

In the next example, Table 6 demonstrates a comparison between sampleswith different concentrations of compatibilizing agent. For example,Comparative B-E and Sample 1-B-E containing 10 wt % compatibilizingagent each exhibit modest changes in physical properties over Reference1-E, but a clear reduction in impact resistance when compared to otherformulations containing reduced amounts of compatibilizing agent(Comparative C-E and Sample 2-A-E, for example).

TABLE 6 Sample compositions and analysis results ASTM- Internal ASTMASTM 1927 method ASTM D-790 D-256 % % D-1693 Flexural IZOD impactBarrier Barrier ESCR modulus resistance Samples to O2 to VOC (h) (MPa)at 23° C. Reference 1-E — 0 180 1273 313 Comparative C-E — 1 95.7 1282356 Comparative B-E — 2 110 1076 170 Sample 1-B-E — 34 600 1058 168Sample 2-A-E — — >1000 1051 356 Sample 3-A-E — — >1000 1237 303

Table 7 demonstrates the effect of crosslinking agent concentration onthe material properties. It can be noted that, with the reduction of thecrosslinking agent content, the module of the resin increases, oftenreturning to the same level of the reference composition. Results fromTable 6 and 7 show that the properties of the materials, and in effectthe PBI, may be tuned by varying the concentration of compatibilizingagent and crosslinking agent and, in some embodiments, polymer blends inaccordance with the present disclosure may exhibit an increase in ESCRwhile maintaining a stiffness and impact resistance relative to therespective reference composition.

TABLE 7 Sample compositions and analysis results. ASTM ASTM ASTM D-790D-256 D-1693 Flexural IZOD impact ESCR modulus resistance at Samples (h)(MPa) 23° C. (J/m) Sample 2-A-E >1000 1051 356 Sample 3-A-E >1000 1237303 Sample 3-B-E >1000 1258 304 Sample 3-C-E >1000 1272 315

Example 3

Selected samples were also evaluated by SEM to analyze the stability ofthe polymer formulations. SEM images for Comparative C-E are shownbefore (FIG. 1) and after (FIG. 2) exposure to boiling water for 2 hoursand, as demonstrated, the polar polymer PVOH is removed from the matrixthrough exposure to boiling water for 2 hours. For samples containingcrosslinking agent, FIG. 3 depicts Sample 1-B-E (with 3% of crosslinkingagent), FIG. 4 depicts Sample 3-A-E (with 0.5% of crosslinking agent),and FIG. 5 depicts Sample 3-C-E (with 1.5% of crosslinking agent), allafter exposure to boiling water for 2 hours. As demonstrated in allcrosslinked samples, the polar polymer particles become non-extractablefollowing crosslinking as evidenced by the decreased solubility of thepolar polymer after boiling.

Example 4

In the next example, the effect of the concentration of polar polymerPVOH and crosslinking agent was analyzed in comparison to the Referenceand Comparative formulations. Results of analytical testing are shown inTable 8.

TABLE 8 Comparative results varying the content of PVOH. ASTM ASTM ASTMD-790 D-256 D-1693 Flexural IZOD impact ESCR modulus resistance atSamples (h) (MPa) 23° C. (J/m) Reference 1-E 180 1273 313 ComparativeC-E 95.7 1282 356 Sample 4-B-E 800 1204 247 Sample 4-C-E >1000 1231 280Sample 3-A-E >1000 1337 303

With particular respect to FIG. 6, the change in ESCR as a function ofPVOH content is demonstrated. Comparative results between purepolyethylene and blends with different PVOH contents are shown, with orwithout crosslinking agent, where the percentage values inside the barsindicate the polar polymer PVOH content. As demonstrated, the ESCR forthe polymer compositions increases with increasing crosslinked PVOHcontent, with the addition of 3% of crosslinked PVOH (Sample 4-B-E)producing a notable increase in ESCR over the reference composition. Forother PVOH contents, the polymer compositions exhibit a continuedincrease in ESCR, while retaining stiffness (as measured by flexuralmodulus) and impact resistance levels, as indicated in Table 8. By wayof contrast, for other technological solutions to improve ESCR to thelevels demonstrated in Table 8, such as increasing molar weight of thepolymers or adding comonomers, the final compositions show acorresponding decrease in stiffness and impact resistance balance.

With particular respect to FIG. 8, the PSI for each of the referencepolyolefins HDPE 1, HDPE 2, and HDPE 3 is shown. With respect to FIG. 8,the PBI is shown for various samples based on Reference 1-E (HDPE 1polyolefin) and containing selected concentrations of crosslinked polarpolymer. As demonstrated in FIG. 8, the PBI increases in samplesformulated with a crosslinked polar polymer, indicating an increase inESCR for the samples in combination with sustained mechanicalproperties.

With particular respect to FIG. 9, a graph is presented showing acomparison of different types of polyolefin, HDPE 1, 2, and 3 referencepolymers with sample polymer compositions modified with 7% of PVOH and0.5% of crosslinking agent and 1% of compatibilizing agent. FIG. 9demonstrates that an N_(PBI) for all studied polyolefin systems over therespective reference polymers.

Example 5

In this example, the modality of the polyethylene molecular weightdistribution is evaluated. Monomodal sample Reference 1-E and thecounterpart Sample 3-A-E containing a crosslinked polar polymer areshown in comparison to bimodal samples Reference 3-E and Reference 4-E,and the respective compositions Sample 5-A-E and Sample 6-A-E containinga crosslinked polar polymer in Table 9.

TABLE 9 Comparative results varying the high density polyethylene(monomodal and bimodal). ASTM ASTM ASTM D-790 D-256 D-1693 Flexural IZODimpact ESCR modulus resistance at Samples (h) (MPa) 23° C. (J/m)Reference 1-E 180 1273 313 Sample 3-A-E >1000 1337 303 Reference 3-E 1501100 168 Sample 5-A-E >1000 1112 163 Reference 4-E 14 1629 150 Sample6-A-E 66 1568 119

As demonstrated in Table 9, the increase in ESCR is relativelyinsensitive of the modality of the molecular weight distribution, andthe sample compositions maintain mechanical properties similar to thatof the respective reference composition. This is possible due to theselective crosslinking of the dispersed phase, maintaining thepolyethylene matrix intact.

Example 6

In the next example, the impact of the reference polymer density on themechanical properties of the polymer compositions is evaluated.Reference 3-E is a polyolefin with density of 0.95 g/cm³ and Reference4-E is a polyolefin with an initial density of 0.96 g/cm³.

It is noted that the selective modification of the PVOH by thecrosslinking agent keeps the mechanical properties of the polymercompositions close to their reference, with the advantage of expressivegains in ESCR for the HDPE 2 resin in Reference 3-E. In spite of the lowvalues with the HDPE 3-based polymer compositions, the relative increasewas superior to 4× the time for ESCR tests than for its pure resin. Theresults are presented in Table 10.

TABLE 10 Comparative results varying the density of the referencepolymer. ASTM ASTM ASTM D-790 D-256 D-1693 Flexural IZOD impact ESCRmodulus resistance at Samples (h) (MPa) 23° C. (J/m) Reference 3-E 1501100 168 Sample 5-A-E >1000 1112 163 Reference 4-E 14 1629 159 Sample6-A-E 66 1568 119

While a number of polyolefin based compositions are discussed in theprevious examples, the above approach may be applied to otherpolyolefins of varied density and molecular weight to produce polymercompositions exhibiting enhanced environmental stress crackingresistance properties and balanced mechanical properties.

Although the preceding description has been described herein withreference to particular means, materials and embodiments, it is notintended to be limited to the particulars disclosed herein; rather, itextends to all functionally equivalent structures, methods and uses,such as are within the scope of the appended claims. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures. It is theexpress intention of the applicant not to invoke 35 U.S.C. § 112(f) forany limitations of any of the claims herein, except for those in whichthe claim expressly uses the words ‘means for’ together with anassociated function,

The invention claimed is:
 1. A polymer composition comprising: a polymermatrix comprising a polyolefin; and one or more polymer particlesdispersed in the polymer matrix, wherein the one or more polymerparticles comprise a polar polymer selectively crosslinked with acrosslinking agent, and wherein the one or more polymer particles has anaverage particle size of up to 200 μm; wherein the polymer matrixfurther comprises a functionalized polyolefin present in the range of0.1 wt % to 15 wt %, based in the total mass of the polymer composition,and wherein the polar polymer comprises at least one functional groupselected from the group consisting of hydroxyl, carboxylic acid,carboxylate, ester, ether, acetate, amide, amine, imide, imine, sulfone,phosphone and their derivatives.
 2. The polymer composition of claim 1,wherein the one or more polymer particles has an average particle sizeof up to 50 μm.
 3. The polymer composition of claim 1, wherein thepolyolefin is present in a range of 99.5 wt % and 30 wt %.
 4. Thepolymer composition of claim 1, wherein the polyolefin is present in arange of 99.9 wt % and 90 wt %.
 5. The polymer composition of claim 1,wherein the polyolefin comprises one or more polymers selected from agroup consisting of ethylene homopolymers, copolymers of ethylene andone or more C3-C20 alpha-olefins, propylene homopolymers, copolymers ofpropylene and one or more comonomers selected from ethylene or C4-C20alpha-olefins, heterophasic propylene polymers, olefin terpolymers, andblends thereof.
 6. The polymer composition of claim 1, wherein the polarpolymer is selected from the group consisting of polyvinyl alcohol,ethylene vinyl alcohol copolymer, ethylene vinyl acetate copolymer andmixtures thereof.
 7. The polymer composition of claim 1, wherein thecrosslinking agent is selected from the group consisting of maleicanhydride, maleic acid, itaconic acid, itaconic anhydride, succinicacid, succinic anhydride, succinic aldehyde, adipic acid, adipicanhydride, phthalic anhydride, phthalic acid, glutaraldehyde, theirderivatives and mixtures thereof.
 8. The polymer composition of claim 1,wherein the functionalized polyolefin is a polyolefin functionalizedwith one or more selected from a group consisting of maleic anhydride,maleic acid, acrylic acid, methacrylic acid, itaconic acid, itaconicanhydride, methacrylate, acrylate, epoxy, silane, succinic acid,succinic anhydride, ionomers, and their derivatives.
 9. The polymercomposition of claim 1, wherein the polymer composition presents aNormalized Property Balance Index (N_(PBI)) within the range of 1.5 to10, wherein the N_(PBI) is calculated according to the formula:${N_{PBI} = \frac{{PBI}_{sample}}{{PBI}_{reference}}},$ wherePBI_(sample) is the property balance index for a sample of the polymercomposition, and PBI_(Reference) is the property balance index of areference polymer composition consisting of the polyolefin; and whereinPBI is calculated according to the formula:${{PBI} = \frac{{FM} \times {IR} \times {ESCR}}{10^{7}}},$ where FM isthe stiffness of the sample as determined by secant modulus ofelasticity at 1% deformation according to ASTM D-790 in units of MPa, IRis the IZOD impact resistance according to ASTM D-256 in units of J/m,and ESCR is the environmental stress cracking resistance according toASTM D-1693 in units of h.
 10. The polymer composition of claim 1,wherein the polymer composition presents up to 60% increase in barrierto oxygen when compared to a reference polyolefin according toASTM-1927.
 11. The polymer composition of claim 1, wherein the polymercomposition presents up to 60% increase in barrier to volatile organiccompounds (VOC) when compared to a reference polyolefin.
 12. Amanufactured article comprising the polymer composition of claim
 1. 13.A polymer composition comprising: a polymer matrix comprising apolyolefin; one or more polymer particles dispersed in the polymermatrix, the one or more polymer particles comprising a polar polymerreacted with a crosslinking agent to form a crosslinked polar polymer,wherein the crosslinking agent reacts selectively with one or morefunctional groups present on the polar polymer, and wherein the polarpolymer is crosslinked in the presence of the polymer matrix, andwherein the crosslinking agent is selected from the group consisting ofmaleic anhydride, maleic acid, itaconic acid, itaconic anhydride,succinic acid, succinic anhydride, succinic aldehyde, adipic acid,adipic anhydride, phthalic anhydride, pthalic acid, glutaraldehyde,their derivatives and mixtures thereof.
 14. A polymer compositioncomprising: a polymer matrix comprising a polyolefin; and one or morepolymer particles dispersed in the polymer matrix, wherein the one ormore polymer particles comprise a polar polymer selectively crosslinkedwith a crosslinking agent, and wherein the one or more polymer particleshas an average particle size of up to 200 μm, wherein the polymer matrixfurther comprises a functionalized polyolefin present in the range of0.1 wt % to 15 wt %, based in the total mass of the polymer composition,and wherein the polar polymer is selected from the group consisting ofpolyvinyl alcohol, ethylene vinyl alcohol copolymer, ethylene vinylacetate copolymer and mixtures thereof.